Regenerative amplifiers



April 7, 1959 w.`c. BROWN 2,881,270

REGENERATIVE AMPLIFIERS Filed Jan. 8, 1958 2 Sheets-Sheet 1 /Z MA 7291/50 S/G/VAL C TEP/MMM 770A/ /3 IMPL /F/EQ Z o TTOIQ/VY (April 7, 1959 w. c. BROWN 2,881,270

REGENERATIVE AMPLIFIERS 2 sheetssheet 2 Filed Jan. 8, 1958 .7N Vs/v TOR WML/AM C. @Row/v 4 free/v5 Y 2,881,270 Patented Apr. 7, 1959 2,881,270 REGENERATIV E AMPLIFIERS William C. Brown, Weston, Mass.,

Manufacturing Company, tion of Delaware Application January `8, 1958, Serial No. 707,809

Claims. (Cl. 179-171) assignor to Raytheon Waltham, Mass., a corpora- This invention relates to regenerative amplifiers and Amore particularly to magnetron amplifiers operated with positive feedback.

Magnetron ampliers arranged to pass a continuous beam of electrons past a series of cavities formed inthe anod'e'about the cathode with their ends isolated arranged `to-amplify radio frequency energy introduced at one end of the line and extracted at the other have been described in an article entitled Platinitron Increases Search Radar Range by the applicant in Electronics for August 1, 1957, beginning at page 164. Considerable power gain can be obtained with such amplifiers over a broad band of frequencies with considerable e'iciency. Bythe 'use vof the construction of this invention it has been found 'possible to increase eiciency and power gain at the expense of band width. This has been accomplished 'by introducing positive feedback, preferably by inserting vmismatches inthe input and output transmission lines at such distances from the input and output of the 'internal delay line or anode that radio frequency energy will be reected from the mismatch in the output line -a'rid `returned to the mismatch in the input line where it is again reected to arrive at the input to the internal delay line in such phase as to be added to the input energy 1in phase. This rellection and rereection is repeated until saturation is reached. Maximum efficiency vand power gain can be obtained over a band width of 1/2 of 1 percent of the operating frequency.

Other and further advantages of this invention will be apparent as the description thereof progresses, reference being had to the accompanying drawings wherein:

Fig. 1 is a highly schematic diagram of the regenerative amplilier of the invention;

Fig. 2 is a vector diagram illustrating the operation of the invention;

Fig. 3 is a schematic diagram of an embodiment of the invention; and

Fig. 4 is an isometric View of an amplifier of the invention.

In Fig. l the reference numeral designates the amr plier of the invention, preferably of the magnetron type, having an input transmission line 11 and output transmission line 12 terminated by a load 13. 'Ihere is a mismatch or discontinuity in the input line represented by the dotted line 14 and another mismatch in the output line represented by the dotted line 15.

The driving signal represented by the arrow 16 in Fig. 1 applied through the line 11 to the amplifier 10 is represented by the vector 20 in Fig. 2 and has an amplitude B and reference phase 0 after passage through the amplifier 10 where-it is amplified. The driving'sgnal is Vreflected by the mismatch back through the amplifier lo'andreected .again from the mismatch 14. This reliected signal .is represented by the vector 21 of amplitude A and phase 0K.

lwhere r1 the-reflection factor kat the output mismatch, r2 =-thelreection factor at vthe input mismatch.

These reection factors are related to the characteristic impedance, Z0, of the output line 11 and to the impedance, Z1, of the output mismatch section 1S as follows:

r2 is computed in a similar manner for the input mismatch. y g1 is the gain of the tube.

'Thel phase wherein 20p is the phase shift caused by two passengers throughthe amplitier; Zat is the phase shift caused by two-passages through the sections of transmission line between the mismatches. 01 is the phase shift caused by the mismatch in the output and 02 is the phase shift caused by the mismatch in the input. N is the nearest integer which will place 0K in the range 180 This signal combines vectorily with the input signal Be10 to produce a second input signal represented by the vector 22 of value C and phase al. This signal is reected twice to become AeiUvl-QK) represented by vector 23 and is vectorily added to the original input signal represented by vector 20 to produce a resultant signal Deiae represented by vector 24. This signal is reflected twice to become signal Ae1`(2+0x) represented by vector -25 which when vectorily added to signal B produces resultant signal fEeina represented by vector 26. This process continues with continually decreasing phase shift until a reflection signal AeNHWK) represented by vector 27 is produced and combined with the input signal to produce resultant signal Teoat represented by vector 28.

A representative arrangement for obtaining these phase shifts and positive feedback is shown schematically in Figs. 3 and 4. A magnetron amplifier 30 is composed of a cathode 31 and anode 32 with vanes 33 forming resonant cavities, with alternate vanes joined kbystraps 34 and 35 with a magnetic lield parallel to the axis of the cathode by means of a magnet 35, means for inserting and driving signal such as the coaxial cable 36 indicated and means for extracting the amplified energy such as the coaxial'cable 37. Energy may be inserted and extracted from the anodeV line in the manner shown in my copending application No. 706,812, filed January 2, 1958. These cables each have a tubular insert 38 or 40 of dielectric material selected and dimensioned to present an impedance .Z1 or Z2 different from the characteristic impedance ofthe coaxial line 36 or 37 to produce the reflectionfactors r1 and r2 according to Equation 1. The position of the mismatches 38 and 40 with respect to the magnetron'30 determines the phase shifts 0i., and the dimensions Vand characteristics of mismatches themselves determine the phase shifts 91 and 92. The phase difference B between the nal reretlected signal and the resultant can be shown to be equal to 0K, the phase angle of first rereected signal so that gli-112:@ (0.2) (0.2) :0.16

A sin at= sin 0K normalized to the input signal,

sin K=O.16 and a-9.2. Even with a power gain of 100, at would need to be only 23.6. With 0K=at and at=sin at where K=fraction of steady state at achieved in time tr. t,=elapsed time normalized to the time required for a round trip between the input and output reections.

A=magnitude of reection vector. B=magnitude of driving signalvector.

If vector A=1B and 2,:3, K=0.963 and if A=0.16B and t,=2, K=O.981.

The device of the invention may be used as a regenerative amplier by adjusting the distance between the input and output reflections by means of a slot 41 and handle 42 so that oscillation occurs without the presence of a driving signal at the same frequency as the initial value of the driver frequency, fo. The frequency of the driving frequency may be changed while retaining the regenerative eiect if the angle 0K is changed according to the relationship where A0K=change in phase of reected wave. Aff-change in frequency of the driving signal.

df is assumed to be independent of frequency and 0K is assumed to be equal to zero when Afd=0, then 0 @FAH-QJ? (n Substituting this value of 0K in Equation 4,

Af= df sin-l-llsin a,

where |B1=driving signal vector magnitude.

lAl=rereection signal vector magnitude.

ai=angle between the driving signal vector B and the input signal vector A+B under steady state conditions.

lRi

g1 1A1+|Bx where: \R|=magnitude of output signal. |B|=magnitude of driver signal. iAl=magnitude of rereected signal.

Combining (l0) and (1l) gives A B ga {li- I iB-lt l Gains in the order of 30 db can be obtained with bandwidths of the order of 1/2 percent.

The operating frequency of the system can be made to be mechanically tunable over a 10 percent range by any of the well-known methods if in addition the mechanism is provided for sliding one of the mismatches in the transmission line to vary the separation between mismatches.

This completes the description of the embodiment of the invention illustrated herein. However, many modications and advantages thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. Accordingly, it is desired that this invention not be limited to the particular details of the embodiment disclosed herein except as defined by the appended claims.

What is claimed is:

1. A regenerative amplier comprising an electron discharge device having a cathode, an anode formed with a delay line terminated by mismatching impedances with ends isolated from each other, means to maintain the anode at a positive potential with respect to the cathode, means for producing a magnetic field in the space between the anode and the cathode in a direction parallel to the axis of the cathode to form a continuous electron beam about the cathode, means for introducing radio frequency energy at one end of the delay line and means for extracting this energy from the other end, the mismatched terminations of the line being disposed a distance apart such that radio frequency energy introduced at one end of the delay line, reilected from the output termination of the line and rereflected from the input end termination of the line will be in phase with the incoming energy.

2. A regenerative amplifier comprising an electron discharge device having a cathode, an anode formed with a delay line terminated by mismatching impedances with ends isolated from each other, means to maintain the anode at a positive potential with respect to the cathode, means for producing a magnetic eld in the space between the anode and the cathode in a direction parallel to the axis of the cathode to form a continuous electronl beam about the cathode, coaxial transmission line means for introducing radio frequency energy at one end of the delay line and coaxial transmission line means for extracting this energy from the other end, the mismatched terminations of the line being disposed a distance apart such that radio frequency energy introduced at one end of the delay line, reilected from the output termination of the line and rereected from the input end termination of the line will be in phase with the incoming energy.

3. A regenerative amplifier comprising an electron discharge device having a cathode, an anode formed with a delay line terminated by mismatching impedances with ends isolated from each other, means to maintain the anode at a positive potential with respect to the cathode, means for producing a magnetic field in the space between the anode and the cathode in a direction parallel to the axis of the cathode to form a continuous electron beam about the cathode, means for introducing radio frequency energy at one end of the delay lline and means for extracting this energy from the other end, the mismatched terminations of the line being formed as tubes of a material presenting a dilerent impedance to the radio frequency energy than the characteristic impedance of the lines disposed a distance apart such that radio frequency energy introduced at one end of the delay line, reilected from the output termination oi the line and rereected from the input end termination of the line will be in phase with the incoming energy.

4. A regenerative amplier comprising an electron discharge device having a cathode, an anode formed with a delay line terminated by mismatching impedances with ends isolated from each other, means to maintain the anode at a positive potential with respect to the cathode, means for producing a magnetic eld in the space between the anode and the cathode in a direction parallel to the axis of the cathode to form a continuous electron beam about the cathode, coaxial transmission line means for introducing radio frequency energy at one end of the delay line and coaxial transmission line means for extracting this energy from the other end, the mismatched terminations of the line being formed as tubes of a material presenting a dilerent impedance to the radio frequency energy than the characteristic impedance of the lines disposed a distance apart such that radio frequency energy introduced at one end of the delay line, reected from the output termination of the line and rereected from the input end termination of the line will be in phase with the incoming energy.

5. A regenerative amplifier comprising an electron discharge device having a cathode, an anode formed with a delay line terminated by mismatching impedances with ends isolated from each other, means to maintain the anode at a positive potential with respect to the cathode, means for producing a magnetic field in the space between the anode and the cathode in a direction parallel to the axis of the cathode to form a continuous electron beam about the cathode, means for introducing radio frequency energy at one end of the delay line and means for extracting this energy from the other end, the mismatched terminations of the line being formed as tubes of a material presenting a different impedance to the radio frequency energy than the characteristic impedance of the lines disposed a distance apart such that radio frequency energy introduced at one end of the delay line, reiected from the output termination of the line and rereected from the input end termination of the line will be in phase with the incoming energy, means for mounting one said mismatch at a variable distance from the delay line.

No references cited. 

